KR20090013204A - Method for producing pentafluoroethane - Google Patents

Abstract

The invention relates to a method for producing pentafluoroethane, and especially to a method comprising (i) a step during which perchloroethylene and optionally 2,2-dichloro-1,1,1-trifluoroethane and/or 2-chloro-1,1,1,2-tetrafluoroethane react(s) with hydrofluoric acid in a gaseous phase in the presence of a catalyst in an adiabetic multi-stage reactor, and optionally (ii) a step of separating the flow produced in step (i) in order to obtain a fraction of light products and a fraction of heavy products.

Description

Method for producing pentafluoroethane {METHOD FOR PRODUCING PENTAFLUOROETHANE}

The present invention relates to a method for producing pentafluoroethane, and more particularly to a method for producing pentafluoroethane by reacting perchloroethylene (PER) with hydrofluoric acid (HF) in the gas phase in the presence of a catalyst. It is about.

Reactions of fluorinating perchloroethylene with HF in the gas phase in the presence of a catalyst are known. Typically the reaction is carried out with 2,2-dichloro-1,1,1-trifluoroethane (123), 2-chloro-1,1,1,2-tetrafluoroethane (124) and pentafluoroethane ( 125), leading to the formation of 123 as the main product.

Such compounds (hereinafter, generally designated by the expression "120 series") are substituted for chlorofluorocarbons (CFCs) in the field or coolers of foams (swelling agents and insulations) or aerosols (propellants), or such All may be used as intermediates for the synthesis of the components. Effective methods for the industrial production of pentafluoroethane are currently being sought.

Since the reaction of perchlorethylene to pentafluoroethane is a strong exothermic reaction (25-30 Kcal / mol), its use on an industrial scale has many problems: the reaction is difficult to control, the catalyst decomposes and by-products This is formed in large quantities.

Document EP 687660 relates to a first reaction zone in which perchlorethylene reacts with hydrogen fluoride at a temperature of 200 ° C. to 450 ° C. under an absolute pressure of 3 to 30 bar, in the gas phase in the presence of a catalyst, and 2,2-dichloro-1,1,1-trifluoroethane and / or 2-chloro-1,1,1,2-tetrafluoroethane contained in the prepared gas with hydrogen fluoride up to 5 bar The reaction takes place in two reaction zones comprising a second reaction zone which reacts in the vapor phase in the presence of a catalyst at a temperature of 250 ° C. to 500 ° C. under an absolute pressure of (the first reaction zone is the pressure of the second reaction zone Maintained at a pressure exceeding) is disclosed a process for preparing pentafluoroethane.

The document EP 754170 discloses (i) perchlorethylene by gas phase contacting hydrogen fluoride with a primary fluorination catalyst comprising chromium oxide, wherein the formula C ₂ H ₁ Cl _{1 + x} F _{1 + y} (where , x and y are each independently 0, 1, 2 or 3 and x + y is understood to be 3) to form a stream of product comprising hydrochlorofluoroethane, and (ii) The stream of product from (i) is subjected to a secondary fluorination catalyst comprising hydrogen fluoride and zinc and / or nickel compounds supported on zinc and / or nickel or on chromium oxide, chromium fluoride or chromium oxyfluoride. Described is a method of making pentafluoroethane comprising the step of making pentafluoroethane by contacting in the presence of a gas phase.

The present invention provides a process for preparing pentafluoroethane from perchloroethylene that can partially or completely solve the above-mentioned drawbacks.

The process according to the invention is characterized in that it comprises the step of reacting perchloroethylene with hydrofluoric acid in the gas phase in the presence of a catalyst in an adiabatic multilayer reactor.

Preferably, the temperature at the inlet of the first layer of the adiabatic reactor is between 280 and 350 ° C, advantageously between 320 and 340 ° C. The temperature at the inlet of the next layer of the adiabatic reactor may also be in the range of 280 to 350 ° C, preferably 320 to 340 ° C.

In this layer, the temperature at the inlet is typically lower than the temperature at the outlet. Moreover, the temperature at the inlet of the previous layer is preferably lower than the temperature at the inlet of the next layer.

The process according to the invention is advantageously carried out in such a way that the temperature in the adiabatic multilayer reactor is below 410 ° C, preferably below 380 ° C.

The adiabatic reactor may comprise 2 to 6 layers. However, it is preferable that the number of layers is 2-4.

The fluorination step can be carried out at a wide range of pressures, but is preferably operated at an absolute pressure of 1 to 10 bar, and advantageously 1 to 4 bar.

The reactants are pre-gassed prior to the fluorination step and are preferably vaporized and preheated to a temperature below the temperature of the adiabatic reactor, and advantageously from 320 to 340 ° C.

Most, preferably more than 90% by weight, of the vaporized and preheated reactants are introduced at the inlet of the first bed of the reactor. A small portion, preferably less than 10% by weight, of the vaporized and preheated reactant, preferably reactant preheated to a temperature of 150 to 200 ° C., is introduced at the inner layer level to better control the temperature of the adiabatic reactor. Preferably, the preheated reactant introduced at the inlet of the first bed of the reactor is at a temperature above the temperature of the reactant introduced at the inner-bed level.

According to one embodiment of the invention, the stream passing through the adiabatic multi-layer reactor is subjected to a separation step such that a fraction of the light product, for example pentafluoroethane and hydrogen chloride, and a fraction of the heavy product, for example Unreacted perchloroethylene, unreacted hydrofluoric acid, and intermediate compounds, especially 2,2-dichloro-1,1,1-trifluoroethane (123), and 2-chloro-1,1,1 , 2-tetrafluoroethane (124) is obtained. The fraction of the heavy product after vaporization and preheating is then recycled to the reactor.

When a fraction of the heavy product is recycled to the reactor, in addition to perchloroethylene, 2,2-dichloro-1,1,1-trifluoroethane and 2-chloro-1,1,1,2-tetrafluoroethane The same intermediate compound also reacts with hydrofluoric acid.

The method may be carried out continuously or batchwise, but is preferably carried out continuously.

The molar ratio of HF / organic reactant is usually 5 to 50, preferably 10 to 30, and advantageously 10 to 20.

The contact time, calculated as the time it takes for the gas to pass through a large amount of catalyst (under reaction conditions), is preferably 5 to 40 seconds, advantageously 10 to 20 seconds.

If the pressure in the fluorination step is below 4 bar absolute, it is sometimes advantageous to compress the reaction product before applying it to the separation step. The compression can be carried out using a compressor, for example in the case of distillation, the separation can be carried out under favorable energy conditions. Moreover, more than 99% of unreacted hydrofluoric acid can be recovered.

Any fluorination catalyst may be suitable for the process of the present invention. The catalyst used preferably comprises oxides, halides, oxyhalides or inorganic salts of chromium, aluminum, cobalt, manganese, nickel, iron or zinc and can be supported. For example, alumina, aluminum fluoride or aluminum oxyfluoride may be mentioned as a support.

Chromium oxide (Cr ₂ O ₃ ) -based catalysts which are in an oxidation state of more than zero and optionally comprise other metals selected from Ni, Co, Mn and Zn are preferably used. Advantageously, the catalyst can be supported on alumina, aluminum fluoride or aluminum oxyfluoride.

Mixture catalysts consisting of nickel oxide, halides and / or oxyhalides and chromium oxides, halides and / or oxyhalides supported on a support consisting of aluminum fluoride or a mixture of aluminum fluoride and alumina are particularly suitable for the process of the invention. May be appropriate.

  The catalyst can be prepared from known activated alumina by known methods. The activated alumina is in the first stage aluminum, by fluorination with hydrofluoric acid, typically at a temperature of 200 to 450 ° C., preferably 250 to 400 ° C., optionally in the presence of an inert gas such as air or nitrogen. Fluoride, or a mixture of aluminum fluoride and alumina. The support is then impregnated with an aqueous solution of chromium salts and nickel salts or an aqueous solution of chromic acid, nickel salts and chromium-reducing agents such as methanol.

When chromic acid (CrO ₃ ) is used as the chromium precursor, the chromium can be reduced by any means known to those skilled in the art, provided that the technique used is not detrimental to the properties of the catalyst and its activity. Preferred reducing agent is methanol.

As chromium and nickel salts, preference is given to using chlorides, but also other salts such as, for example, oxalate, formate, acetate, nitrate and sulfate, or nickel dichromate, provided such salts are Soluble in an amount of water likely to be absorbed by the support.

The mixed catalyst used in the process according to the invention can also be prepared by directly impregnating alumina with a solution of the chromium and nickel compounds mentioned above. In this case, the conversion of at least a portion of the alumina to aluminum fluoride is carried out during the catalyst-activation step.

Activated alumina used in the preparation of mixed catalysts is a well known product on the market. They are usually prepared by calcining alumina hydrate at a temperature of 300 to 800 ° C. Activated alumina that can be used within the scope of the present invention may contain large amounts of sodium (up to 100 ppm) without harming catalytic activity.

The mixed catalyst is 0.5% to 20% by mass of chromium and 0.5% to 20% by mass of nickel, and preferably 2% to 10% by mass of nickel / chromium atomic ratio in the range of 0.5 to 5, preferably 1 Each metal of may be contained.

Prior to use in the perchloroethylene fluorination reaction, the catalytic solid is previously subjected to the activation process.

The treatment carried out "in place" (in a fluorination reactor) or in a suitable apparatus typically comprises the following steps:

Drying at low temperatures in the presence of air or nitrogen,

A drying step at high temperature (250 to 450 ° C., preferably 300 to 350 ° C.) under nitrogen or air,

Hydrofluoric acid and nitrogen, wherein the HF content is adjusted in such a way that the temperature does not exceed 350 ° C. and terminated under a stream of pure hydrofluoric acid or hydrofluoric acid diluted with nitrogen at a temperature that may range from 450 ° C. or less. Fluorination step at low temperature (180-350 ° C.) with a mixture of.

Although not necessary for the fluorination reaction, it may be advantageous for oxygen to be introduced with the reactants in small amounts. The amount may range from 0.02 mol% to 1 mol% with respect to the reactants entering the reactor, depending on the operating conditions. Oxygen may be introduced into the reactor either in pure state or diluted with an inert gas such as nitrogen. Oxygen can also be introduced in the form of air. Regardless of the form adopted, the introduction of oxygen can be carried out continuously or sequentially.

The adiabatic reactor can be made from materials that are resistant to corrosive media, including hydrofluoric acid, for example Hastelloy and Inconel.

The process according to the invention provides a good control of the exothermicity of the reaction, so that defects such as early deactivation of the catalyst can be partially or completely avoided. Moreover, the process can be made to obtain very high pentafluoroethane productivity. In addition, the process can be used to recycle unreacted reactants and intermediate compounds without prior purification.

One embodiment of the present invention is described with reference to a single drawing. In a three-layered adiabatic reactor 110 containing a pre-activated, optionally supported chromium oxide-based catalyst, on the one hand perchlorethylene (101), hydrofluoric acid (102), and optionally air (103) Gas stream 105 comprising and intermediate compounds recycled from HF, PER and stream 104 on the other hand (mainly 2,2-dichloro-1,1,1-trifluoroethane and 2-chloro- 1,1,1,2-tetrafluoroethane). The gas stream 105 was preheated to 300 ° C. prior to introduction into the reactor and the temperature was maintained at 320 to 340 ° C. at the inlet of the first bed. A second stream of the reactor was fed with a gas stream from the first bed and a reactant preheated to 180 ° C. and optionally a gas stream 106 comprising air. The temperature at the inlet of the second layer was also maintained at 320 to 340 ° C. To the third bed of the reactor was fed a gas stream 107 comprising a gas stream derived from the second bed and a reactant, optionally preheated to 180 ° C., and optionally air. In addition, the temperature at the inlet of the third layer was maintained at 320 to 340 ° C. A gas stream 108 passing through the reactor is sent to the distillation tower 111, so that the fraction 109 of the light product comprising, in particular, pentafluoroethane and HCl, and the HF, PER and intermediate compounds (mainly 2, A fraction of the heavy product comprising 2-dichloro-1,1,1-trifluoroethane and 2-chloro-1,1,1,2-tetrafluoroethane) was calculated. A fraction of the heavy product was passed through the bottom into a distillation column and then recycled to the reactor, while a fraction of the light product was subjected to distillation step 112 to separate HCl from pentafluoroethane. Then pentafluoroethane was purified.

Throughout the reaction, the temperature of the multilayer reactor was maintained below 380 ° C. and the absolute pressure was about 3 bar.

Claims (7)

(i) perchlorethylene and optionally 2,2-dichloro-1,1,1-trifluoroethane and / or 2-chloro-1,1,1,2-tetrafluoroethane in adiabatic multilayer reactor Reacting with hydrofluoric acid in the gaseous phase in the presence of H 2 O and optionally (ii) separating the stream prepared in step (i) to yield a fraction of the light product and a fraction of the heavy product. Method of preparation. 2. The process according to claim 1, wherein the temperature at the inlet of the first layer of the adiabatic reactor is from 280 to 350 ° C., preferably from 320 to 340 ° C. 3. 3. The process according to claim 1, wherein the temperature in the reactor is 410 ° C. or less, preferably 380 ° C. or less. 4. Process according to any of the preceding claims, characterized in that the (absolute) pressure of the fluorination step is 1 to 10 bar, preferably 1 to 4 bar. 5. The process according to claim 1, wherein the fraction of the heavy product is recycled to the reactor. 6. 6. The process according to claim 1, wherein the molar ratio of HF / organic reactant is from 5 to 50, preferably from 10 to 30, advantageously from 10 to 20. 7. The chromium oxide (Cr ₂ O ₃ ) -based catalyst according to any one of claims 1 to 6, wherein the catalyst is in an oxidation state of greater than zero and optionally comprises another metal selected from Ni, Co, Mn and Zn. Method characterized in that.

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